By specifying the type of floating-point linkage and floating-point computations you require, you can determine, from Table 19, the associated compiler command-line options that are available.

softvfp specifies software floating-point linkage. When software floating-point linkage is used, either:

Each of the options --fpu softvfp, --fpu softvfp+vfpv2,--fpu softvfp+vfpv3, --fpu softvfp+vfpv3_fp16, --fpu softvfpv3_d16, --fpu softvfpv3_d16_fp16, --fpu softvfp+vfpv4, softvfp+vfpv4_d16 and softvfp+fpv4-sp specify software floating-point linkage across the whole file. In contrast, the __softfp keyword enables software floating-point linkage to be specified on a function by function basis.

If you use the --fpu option, you need to know the VFP architecture version implemented in the target core. An alternative to --fpu=softvfp+... is --apcs=/softfp. This gives software linkage with whatever VFP architecture version is implied by --cpu. --apcs=/softfp and --apcs=/hardfp are alternative ways of requesting the integer or floating-point variant of the Procedure Call Standard for the ARM Architecture (AAPCS).

To use hardware floating-point linkage when targeting ARM Linux, you must explicitly specify a --fpu option that implies hardware floating-point linkage, for example, --fpu=vfpv3, or compile with --apcs=/hardfp. Hardware floating-point linkage is not supported by the ARM Linux ABI. The compiler issues a warning to indicate this.